linux-kernel - Re: [RFC PATCH v3 1/3] mm: Factor out the pagetable pages account into new helper function

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Date:   Sun, 3 Jul 2022 21:48:13 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 1/3] mm: Factor out the pagetable pages account
 into new helper function



On 7/2/2022 6:15 PM, Mike Rapoport wrote:
> On Fri, Jul 01, 2022 at 04:00:59PM +0800, Baolin Wang wrote:
>>
>>
>> On 6/30/2022 10:11 PM, Mike Rapoport wrote:
>>> On Thu, Jun 30, 2022 at 07:11:14PM +0800, Baolin Wang wrote:
>>>> Factor out the pagetable pages account into new helper functions to avoid
>>>> duplicated code. Meanwhile these helper functions also will be used to
>>>> account pagetable pages which do not need split pagetale lock.
>>>>
>>>> Meanwhile convert to use mod_lruvec_page_state() in case of non-order-0
>>>> page table allocation.
>>>
>>> These are *very* rare. I think only parisc may have non-order-0 pmd and pud
>>> tables.
>>
>> s390 also has non-order-0 page table allocation, but they both do not use
>> the generic page table allocation now.
>>
>>> With that, I'd suggest making use of compound_nr() build time opt-in.
>>
>> After more thinking, I'd prefer to change back to use
>> inc_lruvec_page_state()/dec_lruvec_page_state(), since now no architecures
>> will need non-order-0 page table allocation.
>>
>> After this patchset, I plan to convert parisc and s390 to use generic
>> pagetable allocation, then I will add non-order-0 page table allocation
>> support. Like Matthew suggested, maybe I need change the API to pass the
>> number of pages.
> 
> I think it would be simpler to add proper accounting to s390 and parisc
> versions than make them use the generic allocation functions. Moreover, API
> change to support these cases feels like unnecessary churn to me.

Got it. Thanks.